Hemera/Thinkstock(NEW YORK) -- Babies should start having solid foods no earlier than six months, according to pediatricians. But some mothers seem to be jumping the gun on that recommendation, a new study finds.

Writing in the journal Pediatrics, the Centers for Disease Control and Prevention found that four in ten mothers introduced solid foods to their infants before the age of 4 months.

Mothers who did so told the CDC their babies "seemed hungry" or they wanted to feed their babies something "in addition to breast milk or formula." Others thought their babies were "old enough" for solid foods, while some believed it would help their babies "sleep longer at night" -- a myth.

Doctors say babies should get nothing but breast milk or formula for at least six months.